That will probably be the APP_SECRET, ensure you have an environment variable set in either .env.local or your docker-compose.yml file that sets APP_SECRET to the value from your main server.
Personally here I use Serversideup, do a pull of (my) current Suite image from Suites download, extract it and use env vars and a startup script to do an install if certain Env vars are not set. Then i have a CLI command that runs the repair/rebuild and cache:clear, it installs all the mysql (if a fresh install) and creates initial user etc. taks about 3 minutes to run..
Regards
Mark